It is proposed to examine the relationship between collateral sprouting and recovery of function by investigating the morphological and behavioral changes which follow removal of the sensory and the motor input to the cat spinal cord. We will attempt to elicit collateral sprouting from the intact axons of one system after removal of another system, and to detect sprouting by radioautographic and axon degeneration techniques. We expect to find increases in the terminal fields or even new terminal fields in the previously denervated gray matter due to sprouting of new axons from undamaged systems. Metabolic changes in cells of origin will be determined both by measuring their rate of amino acid uptake and by examining such cells microscopically, in an attempt to find morphological correlates of the increased protein synthesis presumably required by sprouting. We expect to correlate anatomical and behavioral changes by testing and recording electromyographically the reflex and locomotor changes following each lesion. We will attempt not only to describe recovery of function but also to determine, using behavioral criteria, its source, i.e. which of the undamaged systems appears to predominate during the recovery period.